Using bottle jacks to support the car is foolhardy at best . . . just get some good jackstands . . . you're worth it. As for positioning, there are usually jack pads under the chassis visible as circular or squarish metal pads. Otherwise, I'd look for a reinforced crossmember as a stand positioning point, and have them placed as far outboard as possible. Double check with a "shake" test by giving the car a shove and see if there's any movement.